Reference metal layer for setting the impedance of metal contacts of a connector

ABSTRACT

A circuit board has an electrical circuit and a connector that is attached to the circuit board. The connector has metal contacts. A housing of the connector has an embedded reference metal layer that is disposed under a single-ended metal contact or differential metal contacts. The reference metal layer sets the impedance of the single-ended metal contact or the differential metal contacts.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.16/953,673, filed on Nov. 20, 2020, now U.S. Pat. No. 11,297,713, whichis a continuation-in-part of U.S. application Ser. No. 17/070,167, filedon Oct. 14, 2020, now U.S. Pat. No. 11,166,367, which is a continuationof U.S. application Ser. No. 16/750,686, filed on Jan. 23, 2020, nowU.S. Pat. No. 10,849,220, all of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to connectors that may beattached to circuit boards.

2. Description of the Background Art

Components of electrical circuits may be mounted on a circuit board,such as a printed circuit board (PCB). Generally speaking, a PCB has asubstrate comprising metal and dielectric layers. The metal layersinclude signal traces that electrically connect two or more points onthe PCB and a reference plane that provides a reference, such as aground reference.

FIG. 1 is a cross-sectional view of a conventional PCB 104. The PCB 104includes a plurality of signal traces 101, a dielectric layer 103, and areference plane 102. The signal traces 101 and the reference plane 102comprise a metal. The signal traces 101 are on one surface of thedielectric layer 103, and the reference plane 102 is on the opposingsurface of the dielectric layer 103. The distance between the signaltraces 101 and the reference plane 102 is set by the thickness H of thedielectric layer 103.

A differential impedance is the impedance presented by two signal traces101 to a differential signal propagating on the two signal traces 101.Traditionally, the differential impedance is set by adjusting the widthW of the signal traces 101, the thickness T of the signal traces 101,the separation distance S between the signal traces 101, and/or thethickness H of the dielectric layer 103. Embodiments of the presentinvention allow for setting of differential or single-ended impedancewhen parameters for setting the impedance are constrained.

SUMMARY

In one embodiment, an impedance of one or more signal traces of acircuit board is set by forming a first signal trace on a first surfaceof a dielectric layer of the circuit board. A reference plane is formedon a second surface of the dielectric layer. A reference trace is formedwithin the dielectric layer. The impedance of the first signal trace ordifferential impedance of the first signal trace and a second signaltrace may be set by adjusting one or more parameters of the referencetrace.

In another embodiment, a circuit board comprises a dielectric layer; afirst signal trace and a second signal trace formed on a first surfaceof the dielectric layer on an edge connector of the circuit board; areference plane formed on a second surface of the dielectric layer; anda reference trace formed within the dielectric layer and between thereference plane and the first and second signal traces, the referencetrace being configured to set a target differential impedance of thefirst and second signal traces.

In yet another embodiment, an impedance of one or more signal traces ofa circuit board is set by forming a first signal trace on a firstsurface of a dielectric layer of the circuit board. A reference trace isformed on a second surface of the dielectric layer. The impedance of thefirst signal trace or differential impedance of the first signal traceand a second signal trace may be set by adjusting one or more parametersof the reference trace.

In yet another embodiment, a circuit board has an electrical circuit anda connector that is attached to a substrate of the circuit board. Theconnector has metal contacts, where two adjacent metal contacts areconfigured to carry a differential signal.

A housing of the connector has an embedded reference metal layer that isdisposed under and between the differential metal contacts. The width ofthe reference metal layer may be adjusted to set the differentialimpedance of the differential metal contacts.

In yet another embodiment, a circuit board has an electrical circuit anda connector that is attached to a substrate of the circuit board. Theconnector has metal contacts, where a metal contact is configured tocarry a single-ended signal. The single-ended metal contact is adjacentto another metal contact. A housing of the connector has an embeddedreference metal layer that is disposed under the single-ended metalcontact. The reference metal layer is connected to a ground referencewhen the adjacent metal contact is not connected to ground. In thatcase, the width of the reference metal layer may be adjusted to set theimpedance of the single-ended metal contact. The reference metal layermay or may not be connected to a ground reference when the adjacentmetal contact is connected to ground. When the adjacent metal contact isgrounded, the width and/or location of the single-ended metal contactmay be adjusted to set the impedance of the single-ended metal contact.

These and other features of the present invention will be readilyapparent to persons of ordinary skill in the art upon reading theentirety of this disclosure, which includes the accompanying drawingsand claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional PCB.

FIG. 2 is a side view of a PCB in accordance with an embodiment of thepresent invention.

FIG. 3 is a zoom-in view of a connector of the PCB of FIG. 2 inaccordance with an embodiment of the present invention.

FIG. 4 is a cross-sectional view of the PCB of FIG. 2 in accordance withan embodiment of the present invention.

FIGS. 5 and 6 are three-dimensional views that illustrate theorientation of signal traces relative to a reference trace of the PCB ofFIG. 2 in accordance with an embodiment of the present invention.

FIG. 7 is a graph of differential impedance in a first case studyperformed by the inventors.

FIG. 8 is a zoom-in view of a connector in a second case study performedby the inventors.

FIG. 9 is a graph of differential impedance in the second case studyperformed by the inventors.

FIG. 10 is a zoom-in view of a connector in a third case study performedby the inventors.

FIG. 11 is a graph of differential impedance in the third case studyperformed by the inventors.

FIG. 12 is a flow diagram of a method of setting a differentialimpedance of differential signal traces in accordance with an embodimentof the present invention.

FIG. 13 is a cross-sectional view of a PCB in accordance with anembodiment of the present invention.

FIG. 14 is a flow diagram of a method of setting a differentialimpedance of differential signal traces in accordance with an embodimentof the present invention.

FIG. 15 is a cross-sectional view of a PCB in accordance with anembodiment of the present invention.

FIG. 16 is a cross-sectional view of a PCB in accordance with anembodiment of the present invention.

FIG. 17 is a side view of a PCB in accordance with an embodiment of thepresent invention.

FIG. 18 is a cross-sectional view of a connector in accordance with anembodiment of the present invention.

FIGS. 19 and 20 are top views of a connector in accordance withembodiments of the present invention.

FIG. 21 is a cross-sectional view of a connector in accordance with anembodiment of the present invention.

FIG. 22 shows a simulation of electromagnetic field lines generated by adifferential signal carried by differential metal contacts of aconnector with a reference metal layer in accordance with an embodimentof the present invention.

FIG. 23 is a three-dimensional view of a portion a connector withdifferential metal contacts and a grounded reference metal layer inaccordance with an embodiment of the present invention.

FIGS. 24 and 25 are three-dimensional views of the top side and bottomside, respectively, of the connector of FIG. 23 for simulation modelingpurposes in accordance with an embodiment of the present invention.

FIG. 26 is a graph of differential impedance of differential metalcontacts in the simulation model of FIGS. 24 and 25 .

FIG. 27 is a three-dimensional view of a portion a connector that hasdifferential metal contacts and an electrically floating reference metallayer in accordance with an embodiment of the present invention.

FIGS. 28 and 29 are three-dimensional views of the top side and bottomside, respectively, of the connector of FIG. 27 for simulation modelingpurposes in accordance with an embodiment of the present invention.

FIG. 30 is a graph of differential impedance of differential metalcontacts in the simulation model of FIGS. 28 and 29 .

FIG. 31 is a three-dimensional view of a portion of a conventionalconnector with differential metal contacts.

FIG. 32 is a graph of differential impedance of differential metalcontacts of the connector of FIG. 31 .

FIG. 33 is a flow diagram of a method of setting a differentialimpedance of differential metal contacts of a connector in accordancewith an embodiment of the present invention.

FIG. 34 is a three-dimensional view of a portion of a connector with anorphan single-ended metal contact and a grounded reference metal layerin accordance with an embodiment of the present invention.

FIG. 35 is a top view of the connector of FIG. 34 .

FIG. 36 is a cross-sectional view of a connector with an orphansingle-ended metal contact and a grounded reference metal layer inaccordance with an embodiment of the present invention.

FIG. 37 is a flow diagram of a method of setting an impedance of anorphan single-ended metal contact of a connector in accordance with anembodiment of the present invention.

FIG. 38 is a cross-sectional view of a connector with a single-endedmetal contact, an adjacent grounded metal contact, and a reference metallayer in accordance with an embodiment of the present invention.

FIG. 39 is a three-dimensional view of a portion a connector with asingle-ended metal contact, an adjacent grounded metal contact, and agrounded reference metal layer in accordance with an embodiment of thepresent invention.

FIG. 40 is a top view of the connector of FIG. 39 .

FIG. 41 is a three-dimensional view of a portion a connector with asingle-ended metal contact, an adjacent grounded metal contact, and agrounded reference metal layer in accordance with another embodiment ofthe present invention.

FIG. 42 is a top view of the connector of FIG. 41 .

FIGS. 43 and 44 are three-dimensional views of a portion a connectorwith a single-ended metal contact, an adjacent grounded metal contact,and a reference metal layer that is not connected to ground inaccordance with embodiments of the present invention.

FIG. 45 is a flow diagram of a method of setting an impedance of asingle-ended metal contact that has an adjacent grounded metal contactof a connector in accordance with an embodiment of the presentinvention.

The use of the same reference label in different drawings indicates thesame or like components. The figures are not drawn to scale.

DETAILED DESCRIPTION

In the present disclosure, numerous specific details are provided, suchas examples of apparatus, components, and methods, to provide a thoroughunderstanding of embodiments of the invention. Persons of ordinary skillin the art will recognize, however, that the invention can be practicedwithout one or more of the specific details. In other instances,well-known details are not shown or described to avoid obscuring aspectsof the invention.

FIG. 2 is a side view of a PCB 200 in accordance with an embodiment ofthe present invention. The PCB 200 includes a connector 201, whichprotrudes from a bottom edge of the PCB 200. As its name indicates, theconnector 201 allows the PCB 200 to be removably connected to anothercircuit board, such as a motherboard or a backplane. In the example ofFIG. 2 , the connector 201 is an edge connector that is removablyinserted into a slot (not shown) of the other circuit board. Theconnector 201 comprises a plurality of signal traces 203 (shown in FIG.3 ), which in the example of FIG. 2 are contact fingers that contactcorresponding pins of the slot. The connector 201 may include one ormore notches 202. A notch 202 prevents incorrect insertion of theconnector 201 into the slot.

FIG. 3 is a zoom-in view of the connector 201 in accordance with anembodiment of the present invention. In the example of FIG. 3 , areference trace 204 is formed directly below adjacent signal traces 203,which are referred to herein as “differential signal traces” in thatthey are configured to carry a differential signal.

The reference trace 204 is visible in FIG. 3 for illustration purposesonly. In practice, the reference trace 204 is not readily visiblebecause the reference trace 204 is within a dielectric layer 211 (shownin FIG. 4 ) of the PCB 200. The signal traces 203 interconnect points onthe PCB 200 and electrical components, such as integrated circuits,resistors, capacitors, etc., mounted on the PCB 200. The PCB 200 mayinclude one or more vias 205 to allow the signal traces 203 to be routedto other layers of the PCB 200. The signal traces 203 are contactfingers at least in the connector 201 portion of the PCB 200.

FIG. 4 is a cross-sectional view of the PCB 200 in accordance with anembodiment of the present invention. In the example of FIG. 4 , the PCB200 comprises a dielectric layer 211 having a surface 213 and anopposing surface 212. The signal traces 203 are formed on the surface213 and a reference plane 210 is formed on the surface 212. Thedielectric layer 211 has a thickness H, which in the example of FIG. 4is the distance between the signal traces 203 and the reference plane210. The signal traces 203 and the reference plane 210 comprise a metal.For example, the signal traces 203 and the reference plane 210 may eachcomprise gold or copper. The PCB 200 may have additional layersdepending on the application. For example, the reference plane 210 maybe between the dielectric layer 211 and another dielectric layer (notshown).

In one embodiment, the signal traces 203 are contact fingers of aconnector that must meet specifications of a standard, such as thePeripheral Component Interconnect (PCI) Express bus standard. Somestandards may specify a differential impedance, i.e., the impedancepresented by two signal traces to a differential signal propagating onthe two signal traces. For example, the PCI Express bus standardrequires a target differential impedance of 85 Ohms. A targetdifferential impedance required by a standard may be difficult to meetwhen the width W of the signal traces 203, the thickness T of the signaltraces 203, and/or the thickness H of the dielectric layer 211 cannot beadjusted or has limited adjustability because of electrical ormechanical constraints.

In the example of FIG. 4 , the PCB 200 includes a reference trace 204.As is well-known, a “trace” makes an electrical connection between twoor more points on a PCB, whereas a “plane” is an uninterrupted area ofmetal that covers a layer of PCB. Without any electrical componentmounted on the PCB 200 and in terms of direct current (DC), thereference trace 204, each signal trace 203, and the reference plane 210are isolated from each other, i.e., the resistance between them is veryhigh. The differential impedance of differential signal traces 203 maybe measured using a time domain reflectometer (TDR).

The reference trace 204 may comprise a metal, such as copper. In oneembodiment, the reference trace 204 is formed within the dielectriclayer 211, directly under and between two adjacent signal traces 203that are configured as differential signal traces. The reference trace204 may have a width E that is narrower than a spanning distance Dbetween outer side perimeters of the differential signal traces 203. Thereference trace 204 has a thickness F and is separated from the signaltraces 203 by a depth G. The width E, thickness F, depth G, position ofthe reference trace 204 within the dielectric 211, and/or otherparameters of the reference trace 204 may be adjusted to meet a targetdifferential impedance of the signal traces 203. More particularly,given constant/fixed or limited adjustability of the parameters of thesignal traces 203, dielectric layer 211, and reference plane 210, thedifferential impedance of the differential signal traces 203 may be setto meet a target impedance by adjusting one or more parameters of thereference trace 204. The parameters of the reference trace 204 may beset to meet a target impedance by using suitable electromagnetic fieldsimulation software, such as the ANSYS HFSS software, for example.

FIGS. 5 and 6 are three-dimensional (3D) views that illustrate theorientation of the differential signal traces 203 relative to thereference trace 204 in accordance with an embodiment of the presentinvention. FIGS. 5 and 6 , which do not show the dielectric layer 211,may be a 3D view of the connector 201 shown in FIG. 3 . FIG. 5 is a viewfrom underneath the reference trace 204. As shown in FIG. 5 , thereference trace 204 may have a longitudinal portion 221 that is inparallel with the length of at least the contact finger portions of thedifferential signal traces 203. In the example of FIG. 5 , the referencetrace 204 has a T-shape, with a portion 222 that is perpendicular to thelongitudinal portion 221. FIG. 6 is a view from a top of the signaltraces 203.

The inventors performed several case studies that compare theeffectiveness of the reference trace 204 compared to other ways ofsetting the differential impedance of differential signal traces 203(i.e., two adjacent signal traces 203 that are configured to propagate adifferential signal) to meet a target impedance, which is 85 Ohms in thecase studies. In the case studies, the dielectric layer 211 has a totalthickness of 63.5 mils and a dielectric constant of 3.0, and each of thedifferential signal traces 203 has pad size (i.e., size of the contactfinger portion) of 28×166 mils as per the PCI Express bus standard. Thecase studies were performed using the ANSYS HFSS software. These casestudies are now explained with reference to FIGS. 7-11 .

FIG. 7 is a graph 251 of differential impedance in a first case studyperformed by the inventors. The graph 251 indicates the differentialimpedance of differential signal traces 203 employed as contact fingersand with a reference trace 204 as shown in FIG. 3 . For the case studyof FIG. 7 , the reference trace 204 has a depth G (see FIG. 4 ) of 12.2mils and a width E of 25 mils. In the example of FIG. 7 , the verticalaxis indicates differential impedance in Ohms and the horizontal axisindicates time in picoseconds. As shown in FIG. 7 , the reference trace204 allows for a differential impedance of about 85 Ohms, which is thetarget impedance in this example. The width E of the reference trace 204may be adjusted to tune the differential impedance of the signal traces203.

FIG. 8 is a zoom-in view of a connector 201B in a second case studyperformed by the inventors. The connector 201B is a particularembodiment of the connector 201 of FIG. 3 , but without a referenceplane 210 and without a reference trace 204. In the second case study,the differential impedance of the differential signal traces 203 isconstrained by the thickness H of the dielectric layer 211 and the padsize of the signal traces 203.

FIG. 9 is a graph 256 of differential impedance in the second casestudy. The graph 256 indicates the differential impedance ofdifferential signal traces 203 employed as contact fingers in theconnector 201B of FIG. 8 . In the example of FIG. 9 , the vertical axisindicates differential impedance in Ohms and the horizontal axisindicates time in picoseconds. As shown in FIG. 9 , removing thereference plane 210 and the reference trace 204 yields a differentialimpedance of about 92 Ohms, which is higher than the target impedance of85 Ohms.

FIG. 10 is a zoom-in view of a connector 201C in a third case studyperformed by the inventors. The connector 201C is particular embodimentof the connector 201 of FIG. 3 , but with the reference trace 204replaced with a reference plane 209 underneath all of the signal traces203 of the connector 201. That is, the connector 201C has a referenceplane 210 (as in FIG. 4 ) and a reference plane 209 instead of thereference trace 204. The reference plane 209 is set in the dielectriclayer 211 at a depth G of 29.14 mils from the signal traces 203. In thethird case study, the differential impedance of differential signaltraces 203 is constrained by the limited depth G of the reference plane209 and the fixed pad size of the signal traces 203.

FIG. 11 is a graph 261 of differential impedance in the third casestudy. The graph 261 indicates the differential impedance ofdifferential signal traces 203 employed as contact fingers as in theconnector 201C of FIG. 10 . In the example of FIG. 11 , the verticalaxis indicates differential impedance in Ohms and the horizontal axisindicates time in picoseconds. As shown in FIG. 11 , replacing thereference trace 204 with the reference plane 209 results in adifferential impedance of about 89 Ohms, which is higher than the targetimpedance of 85 Ohms.

FIG. 12 is a flow diagram of a method 300 of setting a differentialimpedance of differential signal traces in accordance with an embodimentof the present invention. In the example of FIG. 12 , the differentialsignal traces are adjacent signal traces that are formed on a firstsurface of a dielectric layer (step 301). The dielectric layer may bethat of a PCB and the differential signal traces may be contact fingerson an edge connector of the PCB. A reference plane is formed on asecond, opposing surface of the dielectric layer (step 302). A referencetrace is formed within the dielectric layer (step 303), between thedifferential signal traces and the reference plane. Each of thereference trace, reference plane, and differential signal tracescomprises a metal. The reference trace is positioned between thedifferential signal traces and may have dimensions that are constrainedwithin outer perimeters of the signal traces.

One or more parameters of the reference trace are adjusted to set thedifferential impedance of the differential signal traces (step 304). Theparameters of the reference trace include the thickness of the referencetrace, the width of the reference trace, the distance of the referencetrace relative to the differential signal traces, and the position ofthe reference trace within the dielectric layer. For example, parametersof the differential signal traces, the reference plane, and thedielectric layer may be fixed or have limited adjustability because ofelectrical or mechanical constraints imposed by a standard. In thatexample, one or more parameters of the reference trace are adjusted toset the differential impedance of the differential signal traces to meeta target impedance required by the standard, while holding theparameters of the dielectric layer, differential signal traces, andreference plane constant.

FIG. 13 is a cross-sectional view of a PCB 200B in accordance with anembodiment of the present invention. The PCB 200B is a particularembodiment of the PCB 200 shown in FIG. 4 . The PCB 200B is the same asthe PCB 200 but without a reference trace 204 within the dielectriclayer 211 and without a reference plane 210 on the opposing surface 212of the dielectric layer 211. Instead, the PCB 200B has a reference trace303 that is formed on the surface 212 of the dielectric layer 211.

More particularly, the PCB 200B comprises the dielectric layer 211 andsignal traces 203 as previously described. A reference trace 303,instead of a reference plane, is formed on the surface 212 of thedielectric layer 211. In the example of FIG. 13 , the reference trace303 is between the signal traces 203, has a thickness K, and has a widthJ that is narrower than the spanning distance D between outer sideperimeters of the adjacent signal traces 203. The thickness K, width J,and the position of the reference trace 303 on the surface 212 may beadjusted to set the differential impedance of the signal traces 203.

FIG. 14 is a flow diagram of a method 350 of setting a differentialimpedance of differential signal traces in accordance with an embodimentof the present invention. In the example of FIG. 14 , the differentialsignal traces are adjacent signal traces that are formed on a firstsurface of a dielectric layer (step 351). The dielectric layer may bethat of a PCB and the differential signal traces may be contact fingersof an edge connector of the PCB. A reference trace is formed on a secondsurface of the dielectric layer (step 352). The reference trace ispositioned between the differential signal traces and may havedimensions that are constrained within outer parameters of the signaltraces. Each of the reference trace and differential signal tracescomprises a metal.

One or more parameters of the reference trace are adjusted to set thedifferential impedance of the differential signal traces (step 353). Theparameters of the reference trace include the thickness of the referencetrace, the width of the reference trace, and the position of thereference trace on the second surface of the dielectric layer. Forexample, parameters of the differential signal traces and the dielectriclayer may be fixed or have limited adjustability because of electricalor mechanical constraints imposed by a standard. In that example, one ormore parameters of the reference trace are adjusted to set thedifferential impedance of the differential signal traces to meet atarget impedance required by the standard, while holding parameters ofthe dielectric layer and the differential signal traces constant.

Embodiments of the present invention have been described above in thecontext of differential signal traces. In light of the presentdisclosure, it can be appreciated that the present teachings can also beapplied to a single-ended signal trace as now described beginning withFIG. 15 .

FIG. 15 is a cross-sectional view of a PCB 200C in accordance with anembodiment of the present invention. The PCB 200C is a particularembodiment of the PCB 200 shown in FIG. 4 .

In the PCB 200C, the reference trace 204 is directly below asingle-ended signal trace 203, i.e., a signal trace that is configuredto propagate a single-ended signal. The signal trace 203 has a width Wand a thickness T. The signal trace 203 is formed on a surface 213 ofthe dielectric layer 211, which has a thickness H. The reference trace204 may have a width E that is narrower or wider than the width W of thesignal trace 203.

One or more parameters of the reference trace 204 are adjusted to setthe impedance of the signal trace 203 to meet a target impedance. Forexample, given constant/fixed or limited adjustability of the parametersof the signal trace 203, dielectric layer 211, and reference plane 210,the impedance of the signal trace 203 may be set to meet a targetimpedance by adjusting one or more parameters of the reference trace204. The parameters of the reference trace 204 include a width E,thickness F, depth G between the reference trace 204 and the signaltrace 203, and the position of the reference trace 204 within thedielectric layer 211. A method of setting an impedance of a single-endedsignal trace 203 may be the same as the method 300 of FIG. 12 , exceptthat the signal trace is single-ended instead of differential.

FIG. 16 is a cross-sectional view of a PCB 200D in accordance with anembodiment of the present invention. The PCB 200D is a particularembodiment of the PCB 200 shown in FIG. 4 . The PCB 200D is the same asthe PCB 200 but without a reference trace 204 within the dielectriclayer 211, without a reference plane 210 on the opposing surface 212 ofthe dielectric layer 211, and with a single-ended signal trace 203instead of differential signal traces. Similar to the PCB 200B of FIG.13 , the PCB 200D includes a reference trace 303 on the surface 212 ofthe dielectric layer 211.

More particularly, the PCB 200D comprises the dielectric layer 211 and asingle-ended signal trace 203. The signal trace 203, which is formed onthe surface 213 of the dielectric layer 211, has a width W and athickness T. The dielectric layer 211 has a thickness H. A referencetrace 303, instead of a reference plane, is formed on the surface 212 ofthe dielectric layer 211. In the example of FIG. 16 , the referencetrace 303 is directly under the signal trace 203, has a thickness K, andhas a width J. The reference trace 303 may have a width J that isnarrower or wider than the width W of the signal trace 203. Thethickness K, width J, and the position of the reference trace 303 on thesurface 212 of the dielectric layer 211 may be adjusted to set theimpedance of the signal trace 203. A method of setting an impedance of asingle-ended signal trace 203 may be the same as the method 350 of FIG.14 , except that the signal trace is single-ended instead ofdifferential.

Instead of having an edge connector, a circuit board may have anexternal connector mounted thereon. This allows the circuit board to beconnected to other circuit boards and circuits in general usingdifferent connectors to meet the requirements of different applications.A reference metal layer may be embedded within the housing of theconnector to set the impedance of single-ended or differential metalcontacts of the connector. Embodiments pertaining to setting theimpedance of differential metal contacts (i.e., impedance presented bythe differential metal contacts to a differential signal), are nowexplained beginning with FIG. 17 .

FIG. 17 is a side view of a PCB 400 in accordance with an embodiment ofthe present invention. The PCB 400 comprises a substrate 402 on which anelectrical circuit 401 is mounted. The electrical circuit 401 maycomprise a solid state drive (SSD), hard disk drive, central processingunit (CPU), network interface, or other circuit.

A connector 410 comprises a plurality of metal contacts 412 and ahousing 414. A metal contact 412 provides an electrically conductiveterminal for making an electrical connection. The metal contact 412 isalso referred to as a “gold finger” in that it is typically made ofgold. In general, the metal contact 412 may comprise gold, copper, orother metal. The housing 414, which comprises an electrical insulator,houses and provides mechanical support to the metal contacts 412.

The connector 410 is an external connector in that, unlike an edgeconnector, the connector 410 is not an integrated part of the PCB 400.Instead, the connector 410 is attached to the PCB 400. The connector 410may be attached to the substrate 402 using fasteners (e.g., nut/bolt,screws), slot arrangements, solder, adhesive, or other ways.Accordingly, different types of connectors 410 may be attached to thePCB 400 to meet the requirements of different applications. In oneembodiment, the PCB 400 has a Non-Volatile Memory Express (NVMe) circuit401 and the connector 410 is a U.2/U.3 connector. As can be appreciated,embodiments of the present invention are applicable to other circuitsboards and connectors.

In the example of FIG. 17 , a reference metal layer 416 (see FIG. 18 )is embedded within the housing 414. The reference metal layer 416 allowsfor setting of the differential impedance of adjacent differential metalcontacts 412. The reference metal layer 416 may comprise gold, copper,or other metal.

FIG. 18 is a cross-sectional view of the connector 410 in accordancewith an embodiment of the present invention. In one embodiment, a metalcontact 412 has a pad portion 417 and a lead portion 418. In the exampleof FIG. 18 , the pad portion 417 is configured to make a removableelectrical connection with a contactor 415 (e.g., cantilever beam) ofanother connector 419. The connector 419 may be mounted on or is a partof another PCB (not shown). The lead portion 418 may be soldered to anelectrical node, e.g., ground or a signal trace, on the PCB 400. Thereference metal layer 416 is disposed within the housing 414. In oneembodiment, the reference metal layer 416 is disposed within a ledgeblock 423 of the housing 414. The reference metal layer 416 may extendout of the housing 414 to allow for connection to ground. In embodimentswhere the reference metal layer 416 is left electrically floating, thereference metal layer 416 does not necessarily have to extend out of thehousing 414. The metal contacts 412 may be disposed on a top surface 424of the ledge block 423.

FIGS. 19 and 20 are top views of the connector 410 in accordance withembodiments of the present invention. In one embodiment, the connector410 includes mounting points that facilitate attachment of the connector410 onto a circuit board. In the example of FIG. 19 , the mountingpoints include one or more mounting holes 425 for securing the connector410 to the circuit board using screws, nut and bolt, etc. Also shown inFIG. 19 are the lead portions 418 and pad portions 417 of metal contacts412. A reference metal layer 416 (not shown) is embedded within theledge block 423 of the housing 414, under the pad portions 417 ofadjacent differential metal contacts 412. The lead portions 418 aresoldered to corresponding electrical nodes on the circuit board.

In the example of FIG. 20 , the mounting points include side slots 427(depicted as dotted lines) that accept corresponding edges of thecircuit board. The lead portions 418 of the metal contacts 412 aresoldered to terminals 426 of the circuit board, which in turn areconnected to electrical nodes on the circuit board. A reference metallayer 416 (not shown) is embedded within the ledge block 423 of thehousing 414, under the pad portions 417 of adjacent differential metalcontacts 412.

FIG. 21 is a cross-sectional view of the connector 410 in accordancewith an embodiment of the present invention. In one embodiment, thereference metal layer 416 is embedded within the housing 414, under andbetween adjacent differential metal contacts 412-2 and 412-3 that areconfigured to carry a differential signal S+/S−. The metal contacts412-1 and 412-4 that are adjacent to the metal contact 412-2 and 412-3,respectively, are connected to ground reference. The metal contacts 412(i.e., 412-1, 412-2, etc.) and the reference metal layer 416 may beconnected to corresponding electrical nodes on the circuit board.

The reference metal layer 416 may have a width (see dimension 431) thatis narrower than a spanning distance between outer side perimeters ofthe metal contacts 412-2 and 412-3 (see dimension 433). In oneembodiment, the ledge block of the housing 414 in which the referencemetal layer 416 is embedded has a thickness (see dimension 432) of 48mil, the reference metal layer 416 is disposed at a depth of (seedimension 430) 7 mil from a top surface of the ledge block of thehousing 414, the housing 414 has a dielectric constant of 3.6, and thereference metal layer 416 has a width (see dimension 431) of 38 mil. Thewidth of the reference metal layer 416 may be adjusted to set theimpedance of the differential metal contacts 412-2 and 412-3.

The reference metal layer 416 may have a thickness (see dimension 434)of 0.6 mil or 1.2 mil. In general, the thickness of the reference metallayer 416 does not appreciably affect the impedance of metal contacts.The reference metal layer 416 may have a rectangular shape (as viewedfrom the top) with dimensions of 38 mil×173 mil (width×length). In oneembodiment, the metal contacts 412 have a pitch of 13.8 mil and each is1.7 mil thick. A metal contact 412 may have a rectangular shape (asviewed from the top) with dimensions of 17.7 mil×173 mil (width×length).The metal contacts 412 and the reference metal layer 416 may haveparallel substantially rectangular shapes.

FIG. 22 shows a simulation of electromagnetic field lines generated by adifferential signal carried by the differential metal contacts 412-2 and412-3. The metal contacts 412-1 and 412-4 are grounded (i.e., connectedto ground reference). As illustrated in FIG. 22 , the reference metallayer 416 affects the electromagnetic field lines generated by thedifferential signal. The width of the reference metal layer 416 may beadjusted to set the differential impedance presented by the metalcontacts 412-2 and 412-3 to the differential signal. The reference metallayer 416 may be electrically floating or grounded to further tune thedifferential impedance. The effect of the reference metal layer 416 tothe differential impedance may be determined and adjusted by using asuitable electromagnetic field simulation software, such as the ANSYSHFSS software, for example.

FIG. 23 is a three-dimensional view of a portion a connector 410A inaccordance with an embodiment of the present invention. The connector410A is a particular embodiment of the connector 410 wherein thereference metal layer is grounded and sets the differential impedance ofdifferential metal contacts. The reference metal layer may be groundedby connecting it to a ground reference on the circuit board. In thefollowing description, the reference metal layer is relabeled as “416A”to indicate that it is connected to ground reference and sets thedifferential impedance of differential metal contacts. The housing 414is depicted as transparent to show the orientation of the referencemetal layer 416A relative to the metal contacts 412 (i.e., 412-1, 412-2,etc.). The reference metal layer 416A is embedded within the housing414, under and between the differential metal contacts 412-2 and 412-3,which are connected to differential signal traces on the circuit board.

FIGS. 24 and 25 are three-dimensional views of the top side and bottomside, respectively, of the connector 410A for simulation modelingpurposes in accordance with an embodiment of the present invention. Inone embodiment, metal plugs 451, which go through vias 450, areconnected to ground reference. The reference metal layer 416A, metalcontact 412-1, and metal contact 412-4 are, in turn, connected to themetal plugs 451. As illustrated in FIG. 25 , the reference metal layer416A may have a T-shape, with a longitudinal portion that is in parallelwith the metal contacts 412 and a perpendicular portion (see 452) thatis perpendicular to the longitudinal portion.

FIG. 26 is a graph 461 of differential impedance of the metal contacts412-2 and 412-3 in the simulation model of the connector 410A shown inFIGS. 24 and 25 . In the simulation model of the connector 410A, thereference metal layer 416A, the metal contacts 412, and the housing 414have characteristics as described above with reference to FIG. 21 . Inthe example of FIG. 26 , the vertical axis indicates differentialimpedance in Ohms and the horizontal axis indicates time in picoseconds.As shown in FIG. 26 , the reference metal layer 416A allows for adifferential impedance of about 84 Ohms, which is close to a targetimpedance of 85 Ohms. The width of the reference metal layer 416A may beadjusted to tune the differential impedance of the differential metalcontacts 412-2 and 412-3.

FIG. 27 is a three-dimensional view of a portion a connector 410B inaccordance with an embodiment of the present invention. The connector410B is a particular embodiment of the connector 410 wherein thereference metal layer is electrically floating, i.e., not electricallyconnected to anything. In the following description, the reference metallayer is relabeled as “416B” to indicate that it is electricallyfloating and sets the differential impedance of differential metalcontacts. The housing 414 is depicted as transparent to show theorientation of the reference metal layer 416B relative to the metalcontacts 412. The reference metal layer 416B is embedded within the bodyof the housing 414, under and between the differential metal contacts412-2 and 412-3, which are connected to differential signal traces onthe circuit board.

FIGS. 28 and 29 are three-dimensional views of the top side and bottomside, respectively, of the connector 410B for simulation modelingpurposes in accordance with an embodiment of the present invention. Themetal plugs 451, which go through vias 450, are connected to groundreference. The metal contacts 412-1 and 412-4 are, in turn, connected tothe metal plugs 451. As illustrated in FIG. 29 , the reference metallayer 416B is electrically floating.

FIG. 30 is a graph 462 of differential impedance of the metal contacts412-2 and 412-3 in the simulation model of the connector 410B shown inFIGS. 28 and 29 . The simulation parameters for the graph 462 are thesame as for the graph 461 of FIG. 26 except that the reference metallayer 416B is electrically floating. In the example of FIG. 30 , thevertical axis indicates differential impedance in Ohms and thehorizontal axis indicates time in picoseconds. As shown in FIG. 30 , thereference metal layer 416B allows for a differential impedance of about84.5 Ohms, which is close to a target impedance of 85 Ohms. The width ofthe reference metal layer 416B may be adjusted to tune the differentialimpedance of the differential metal contacts 412-2 and 412-3.

FIG. 31 is a three-dimensional view of a portion of a conventionalconnector 500. The connector 500 has a plurality of metal contacts 501(i.e., 501-1, 501-2, etc.) that are formed on a surface of a housing502. The metal contacts 501-2 and 501-3 are differential metal contactsthat carry a differential signal S+/S−. The metal contacts 501-1 and501-4 are connected to ground. In contrast to the connector 410, theconnector 500 does not have a reference metal layer. This makes itdifficult to adjust the differential impedance of the metal contacts501-2 and 501-3 to meet a target impedance, especially in applicationswhere the pitch and dimensions of the metal contacts 501 are constrainedby the application.

FIG. 32 is a graph 463 of differential impedance of the metal contacts501-2 and 501-3 as determined by simulation that is similar to thatperformed for the connectors 410A and 410B except without a referencemetal layer. In the example of FIG. 32 , the vertical axis indicatesdifferential impedance in Ohms and the horizontal axis indicates time inpicoseconds. In the example of FIG. 32 , the metal contacts 501-2 and501-3 present a differential impedance of about 115 Ohms, which isrelatively high compared to a target impedance of 85 Ohms. Worse, thereis no easy way to adjust the differential impedance because theparameters of the metal contacts 501 and housing 502 may be constrainedby the application.

FIG. 33 is a flow diagram of a method 550 of setting a differentialimpedance of differential metal contacts of a connector in accordancewith an embodiment of the present invention. In the example of FIG. 33 ,the differential metal contacts are disposed on a surface of a connectorhousing (step 551). A reference metal layer is formed within theconnector housing (step 552), under and between the differential metalcontacts. Each of the reference metal layer and differential metalcontacts comprises a metal. The reference metal layer may havedimensions that do not extend beyond outer side perimeters of thedifferential metal contacts. The reference metal layer and thedifferential metal contacts may have parallel substantially rectangularshapes, with the reference metal layer being narrower than a spanningdistance between outer side perimeters of the differential metalcontacts. The width of the reference metal layer may be adjusted to setthe differential impedance of the differential metal contacts (step553). The reference metal layer may be electrically floating orconnected to ground depending on the application or resultingdifferential impedance of the differential metal contacts (step 554).

A reference metal layer may also be employed to set the impedance ofindividual single-ended metal contacts of a connector as now describedbeginning with FIG. 34 .

FIG. 34 is a three-dimensional view of a portion a connector 410C inaccordance with an embodiment of the present invention. The connector410C is a particular embodiment of the connector 410 wherein thereference metal layer is grounded and sets the impedance of an orphansingle-ended metal contact. A single-ended metal contact is a metalcontract that is configured to propagate a single-ended signal. An“orphan” single-ended metal contact is a metal contact with no adjacentmetal contact that is connected to ground reference.

In the following description, the reference metal layer is relabeled as“416C” to indicate that it is connected to ground reference and isconfigured to set the impedance of an orphan single-ended metal contact.More particularly, in the example of FIG. 34 , the reference metal layer416C sets the impedance presented by the single-ended metal contact412-5 to a single-ended signal. The single-ended metal contact 412-5 isan orphan in that metal the contacts (not shown) that are adjacent tothe metal contact 412-5 are not grounded. In the case of an orphansingle-ended metal contact, the reference metal layer 416C needs to beconnected to ground reference to properly set the impedance of thesingle-ended metal contact. As before, the housing 414 is depicted astransparent to show the orientation of the reference metal layer 416Crelative to the metal contact 412-5. The reference metal layer 416C isembedded within the housing 414, directly under the metal contact 412-5,which is connected to a single-ended signal trace on the circuit board.

FIG. 35 is a top view of the connector 410C, showing the orientation ofthe reference metal layer 416C relative to the orphan single-ended metalcontact 412-5. In the example of FIG. 35 , the reference metal layer416C is centered directly underneath and is wider than the metal contact412-5.

FIG. 36 is a cross-sectional view of the connector 410C in accordancewith an embodiment of the present invention. In one embodiment, thereference metal layer 416C is embedded within the housing 414, directlyunder the metal contact 412-5, which is configured to carry asingle-ended signal S1. The metal contacts 412-6 and 412-7 that areadjacent to the metal contact 412-5 are not grounded, rendering themetal contact 412-5 to be orphan. In the example of FIG. 36 , the metalcontacts 412-6 and 412-7 are configured to carry single-ended signals S2and S3, respectively. The metal contacts 412-5, 412-6, and 412-7 areconnected to corresponding single-ended signal traces on the circuitboard, whereas the reference metal layer 416C is connected to a groundreference on the circuit board. The width of the reference metal layer416C may be adjusted to set the impedance of the orphan single-endedmetal contact 412-5. The metal contacts, reference metal layer, andconnector housing of FIG. 36 may have the same dimensions as in FIG. 21.

FIG. 37 is a flow diagram of a method 600 of setting an impedance of anorphan single-ended metal contact of a connector in accordance with anembodiment of the present invention. In the example of FIG. 37 , metalcontacts are formed on a surface of a connector housing (step 601). Areference metal layer is formed within the connector housing (step 602),directly under an orphan single-ended metal contact. Each of thereference metal layer and single-ended metal contacts comprises a metal.Metal contacts that are adjacent on either side of the orphansingle-ended metal contact are not connected to ground reference. Thereference metal layer and the orphan single-ended metal contact may haveparallel substantially rectangular shapes, with the reference metallayer being wider than the orphan single-ended metal contact. The widthof the reference metal layer may be adjusted to set the impedance of theorphan single-ended metal contact (step 603). The reference metal layeris connected to ground reference (step 604).

FIG. 38 is a cross-sectional view of a connector 410D/E in accordancewith an embodiment of the present invention. In the connector 410D/E, areference metal layer is employed to set the impedance of a single-endedmetal contact that is adjacent to a grounded metal contact. The groundedmetal contact may be on either side of the single-ended metal contact.

More particularly, in the example of FIG. 38 , the reference metal layer416D/E is embedded within the housing 414, under a single-ended metalcontact 412-9, which is configured to carry a single-ended signal S4.The reference metal layer 416D/E may be grounded (labeled herein as“416D”) or left electrically floating (labeled herein as “416E”). Themetal contact 412-9 is adjacent to a metal contact 412-8, which isconnected to ground reference. The width of the reference metal layer416D/E (see dimension 431) and/or the location of the reference metallayer 416D/E within the spanning distance 433 between outer sideperimeters of the single-ended metal contact 412-9 and grounded metalcontact 412-8 may be adjusted to set the impedance of the metal contact412-9. The metal contact 412-9 is connected to a correspondingsingle-ended signal trace on the circuit board, whereas the metalcontact 412-8 is connected to a ground reference on the circuit board.The reference metal layer 416D/E may or may not be grounded depending onthe embodiment. The metal contacts, reference metal layer, and housingof FIG. 38 may have the same dimensions as in FIG. 21 .

FIG. 39 is a three-dimensional view of a portion a connector 410D inaccordance with an embodiment of the present invention. The connector410D is a particular embodiment of the connector 410 wherein thereference metal layer is grounded and sets the impedance of asingle-ended metal contact that is adjacent to a grounded metal contact.The reference metal layer may be grounded by connecting it to a groundreference on the circuit board. In the following description, thereference metal layer is relabeled as “416D” to indicate that it isconnected to ground reference and is configured to set the impedance ofa single-ended metal contact that is adjacent to a grounded metalcontact. More particularly, in the example of FIG. 39 , the referencemetal layer 416D sets the impedance presented by the single-ended metalcontact 412-9 to a single-ended signal. The single-ended metal contact412-9 is adjacent to a grounded metal contact 412-8. A grounded metalcontact may be on either or both sides of the single-ended metal contact412-9. The housing 414 is depicted as transparent to show theorientation of the reference metal layer 416D relative to the metalcontacts 412-8 and 412-9. In the example of FIG. 39 , the referencemetal layer 416D is embedded within the housing 414, directly under themetal contact 412-9, which is connected to a single-ended signal traceon the circuit board.

FIG. 40 is a top view of the connector 410D, showing the orientation ofthe reference metal layer 416D relative to the metal contacts 412-8 and412-9. In the example of FIG. 40 , the reference metal layer 416D iscentered directly underneath and is wider than the metal contact 412-9.The width of the reference metal layer 416D may be adjusted to set theimpedance presented by the metal contact 412-9 to a single-ended signal.

The impedance of the metal contact 412-9 may also be set by adjustingthe location of the reference metal layer 416D between outer sideperimeters of the metal contact 412-9 and the adjacent grounded metalcontact, which is the metal contact 412-8 in this example. This isillustrated in FIG. 41 , which is a three-dimensional view of a portiona connector 410D in accordance with an embodiment of the presentinvention. In the example of FIG. 41 , the reference metal layer 416D isembedded within the housing 414, under and between the single-endedmetal contact 412-9 and the grounded metal contact 412-8.

FIG. 42 is a top view of the connector 410D of FIG. 41 , showing theorientation of the reference metal layer 416D relative to thesingle-ended metal contact 412-9 and the grounded metal contact 412-8.In the example of FIG. 42 , the reference metal layer 416D is centeredbetween the metal contacts 412-8 and 412-9. In general, the referencemetal layer 416D may be located within a spanning distance between outerside perimeters of the metal contacts 412-8 and 412-9 to set theimpedance of the metal contact 412-9. Alternatively or in addition, thewidth of the reference metal layer 416D may be adjusted to set theimpedance of the metal contact 412-9.

FIGS. 43 and 44 are three-dimensional views of a portion a connector410E in accordance with an embodiment of the present invention. Theconnector 410E is the same as the connector 410D of FIGS. 39 and 41except that the reference metal layer, which is relabeled as “416E”, iselectrically floating. FIG. 43 shows the reference metal layer 416E asbeing centered directly underneath the single-ended metal contact 412-9,while FIG. 44 shows the reference metal layer 416E as being centeredbetween the single-ended metal contact 412-9 and grounded metal contact412-8. In general, the reference metal layer 416E may be located withina spanning distance between the single-ended metal contact 412-9 and thegrounded metal contact 412-8 to set the impedance of the single-endedmetal contact 412-9. Alternatively or in addition, the width of thereference metal layer 416E may be adjusted to set the impedance of thesingle-ended metal contact 412-9.

FIG. 45 is a flow diagram of a method 650 of setting an impedance of asingle-ended metal contact that has an adjacent grounded metal contactof a connector in accordance with an embodiment of the presentinvention. In the example of FIG. 45 , metal contacts are formed on asurface of a connector housing (step 651). A reference metal layer isformed within the body of the connector housing, under a single-endedmetal contact and a grounded metal contact that is adjacent to thesingle-ended metal contact (step 652). The reference metal layer may belocated within a spanning distance between outer side perimeters of thesingle-ended metal contact and the grounded metal contact to set theimpedance of the single-ended metal contact (step 653). Alternatively orin addition, the width of the reference metal layer may be adjusted toset the impedance of the single-ended metal contact (step 653). Thereference metal layer may be grounded or left electrically floating(step 654).

Circuit boards, connectors, and methods of setting an impedance ofsignal traces and metal contacts have been disclosed. While specificembodiments of the present invention have been provided, it is to beunderstood that these embodiments are for illustration purposes and notlimiting. Many additional embodiments will be apparent to persons ofordinary skill in the art reading this disclosure.

What is claimed is:
 1. A connector for a circuit board, the connectorcomprising: a housing; a ledge block; a plurality of metal contacts thatare disposed on a surface of the ledge block, each of the plurality ofmetal contacts having a pad portion with a first surface disposed on thesurface of the ledge block and a second surface opposite the firstsurface, the second surface being exposed to make a removable electricalconnection with a contactor of another connector of another circuitboard, adjacent first and second metal contacts of the plurality ofmetal contacts being configured to carry a differential signal; areference metal layer disposed within the ledge block under and betweenthe first and second metal contacts, the reference metal layer having awidth that is narrower than a spanning distance between outsideperimeters of the first and second metal contacts, the reference metallayer being configured to set a differential impedance of the first andsecond metal contacts; and a mounting point for attaching the housing tothe circuit board.
 2. The connector of claim 1, wherein the mountingpoint is a mounting hole on the housing.
 3. The connector of claim 1,wherein each of the plurality of metal contacts comprises: a leadportion that is configured to be connected to an electrical node of thefirst circuit board; and a pad portion that is configured to make theremovable electrical connection with the contactor of the anotherconnector of the another circuit board.
 4. The connector of claim 1,further comprising: a third metal contact of the plurality of metalcontacts; and a fourth metal contact of the plurality of the metalcontacts, wherein the third metal contact is adjacent to the first metalcontact, the fourth metal contact is adjacent to the second metalcontact, and the third and fourth metal contacts are configured to begrounded.
 5. The connector of claim 4, further comprising: a first metalplug that goes through a first via of the housing; and a second metalplug that goes through a second via of the housing, wherein the firstmetal plug is electrically connected to the third metal contact and thesecond metal plug is electrically connected to the fourth metal contact.6. The connector of claim 1, wherein the reference metal layer isconfigured to be electrically floating.
 7. The connector of claim 1,wherein the reference metal layer is configured to be grounded.
 8. Theconnector of claim 1, wherein the reference metal layer has a T-shapewith a longitudinal portion that is in parallel with the first andsecond metal contacts and a perpendicular portion that is perpendicularto the longitudinal portion.